2010 Chevy Malibu

Really want to know what could have happened to car worst case.

2010 Malibu LTZ So dealership first provides 5 quarts of oil for car on oil change 6/29. 7/10 take car back heating up and smells like burning oil/melting plastic. They say car just runs hot didn't find any ting wrong. Reluctantly took car that night smoke was coming from back. Next day went to town 7miles parked for about 20 min. Came out to puddle of oil about 8"across alot. Drove car to cousins 2miles parked checked oil while car was hot still said full. Took car to dealership next day leaked out more in the bay in a 2min or so whole underside of car was covered. They said filter was loose but no worries oil never went below full on dipstick.? But when they said they just replaced filter and cleaned underside of car. Car almost red lined next day. Towed back to dealer but would not authorize work till figured out what had happened the GM was not there. Later looking at Invoice noticed it said while replacing filter and cleaning they add 3Q oil.?? My appology letter clearly said it came in full on dipstick. Went back asked if at the time of that service they had drained any oil from the car they said no just what would have came out in the filter and they topped it off. ??? with 3Q!! No answer for it but I had them document it on my invoice. So moral of story car will not go up hills without heating up well ove half??? My guess is they lied and my car was not full and had actully been ran with only 1 3/4Q - 2Q of oil. What is wrong with my brand new car no one wants to tell me. They just want me to keep driving until it throws a code!!